The present invention relates to a method and apparatus for testing rod-shaped articles which form part of or constitute smokers' products and wherein an open-ended tubular wrapper surrounds a gas-permeable filler which consists of tobacco and/or filter material. More particularly, the invention relates to improvements in a method and apparatus for testing rod-shaped articles, while the articles move sideways past a testing station, by resorting to streams of air or another suitable gaseous testing fluid which is caused to pass through the fillers of articles at the testing station whereby the pressure and/or another characteristic of the streams changes during passage through the fillers of articles with defective fillers and/or wrappers. Such changes in pressure and/or other characteristic or characteristics of the streams can be detected in a manner known per se and used for the generation of signals which effect segregation of defective articles from satisfactory articles.
The quality of plain or filter tipped cigarettes, filter rod sections and analogous rod-shaped articles depends to a large extent on the condition of their wrappers. An open seam and/or a hole in the wrapper warrents segregation of the respective article from other articles before the article with a defective wrapper reaches the storage and/or a packing machine. Therefore, the manufacturers of smokers' products invariably test the articles in order to detect and remove defective articles before they can reach the purchaser or the ultimate user. As a rule, cigarettes or analogous rod-shaped articles are tested with streams of air or another testing fluid which is introduced into one or both ends of a wrapper. If the pressure of the air stream changes to a predetermined extent, the wrapper of the article is likely to be defective and the respective article is automatically segregated from satisfactory articles.
During testing, the stream or streams of testing fluid which are introduced into the wrapper of an article to be tested must be sealed from the surrounding atmosphere because the communication of testing fluid with the surrounding air invariably results in inaccurate measurements and eventual segregation of satisfactory articles. Therefore, the testing fluid is normally introduced through suitable elements which engage the ends of the wrappers and the respective ends of fillers whereby the quality of sealing action depends on the extent to which the sealing elements are pressed against the adjacent ends of the wrappers and/or fillers. The force with which a sealing element is urged against the end of a wrapper cannot be increased at will because the sealing element would be likely to deform and/or deface the article. As a rule, even a very small foreign particle (such as a shred of tobacco or filter material) on that surface of a sealing element which engages the end of a wrapper and/or filler is likely to permit testing fluid to communicate with surrounding air and to distort the measurement of the pressure to such an extent that the respective article is discarded even though its filler and/or wrapper is satisfactory.
It was already proposed to seal the open ends of wrappers from the surrounding atmosphere by jets or currents of a sealing fluid which are directed against the external surfaces of the wrappers in the region of their ends. The currents are directed radially or substantially radially toward the external surfaces of the wrapper ends to form a barrier which prevents direct communication between the streams of testing fluid and the surrounding atmosphere. A drawback of such proposal is that the generation and maintenance of currents of sealing fluid consume substantial amounts of energy and can only be achieved by resorting to complex and bulky sealing devices which are prone to malfunction. Moreover, the generation of currents of sealing fluid takes up a certain amount of time so that such method of testing is not practical in a machine which turns out large quantities of rod-shaped articles per unit of time, e.g., in a machine for the production of plain or filter cigarettes wherein the cigarettes are produced at the rate of up to and in excess of 70 per second.